Toxicity of Malathion and Diazinon Byproducts Generated Through the UV/Nano-Zn Process

The potential toxicity of diazinon and malathion byproducts had been poorly studied. This study aimed to determine the toxicity of malathion, diazinon, and their byproducts generated through the UV/nano-Zn process. Diazinon and malathion samples were prepared at 1, 5, and 10 mg/L concentrations. In this study, the UV/nano-ZnO process was used for the degradation of these insecticides. The contact times in reactors were 0.5, 1, and 2 h and pH was set at 6, 7, 8, and 9. The dehydrogenase enzyme assay using Nitrobacter and Nitrosomonas bacteria was used for malathion, diazinon, and their byproducts. All tests were prepared in triplicate. The probit analysis in SPSS Ver. 16.0 software was used for the calculation of EC50 (50% effective concentrations). According to the results, byproduct analysis and toxicity assessment were performed in the following situation in the UV/nano-ZnO process: pH 8, contact time of 2 h, initial concentration of 5 mg/L, removal efficiency of diazinon and malathion of 95.4% and 97.5%, respectively. The EC50 values using Nitrobacter and Nitrosomonas were 0.35 and 4.26 mg/L for diazinon and 173.3 and 279.82 mg/L for malathion, respectively. The EC50 values using Nitrobacter and Nitrosomonas were 2.24 and 2.82 mg/L for diazinon byproducts and 28.10 and 197.92 mg/L for malathion byproducts, respectively. This study showed that in some cases the byproducts of diazinon and malathion produced through the UV/nano-ZnO process are more toxic than diazinon and malathion (primary forms). Therefore, it can be suggested that their removal in photo-catalyst processes should be under special caution.